Fluoropolymer coating compositions containing adhesive polymers and substrate coating process

ABSTRACT

A liquid fluoropolymer coating composition and a process for using the composition to make fluoropolymer coated polymeric substrates. The liquid fluoropolymer composition comprises fluoropolymer selected from homopolymers and copolymers of vinyl fluoride and homopolymers and copolymers of vinylidene fluoride polymer, solvent, and compatible adhesive polymer comprising functional groups selected from carboxylic acid, sulfonic acid, aziridine, amine, isocyanate, melamine, epoxy, hydroxy, anhydride and mixtures thereof. In the process, the composition is applied to a polymeric substrate comprising functional groups on its surface that interact with said compatible adhesive polymer to promote bonding of said fluoropolymer coating to said substrate. The solvent is removed from the coating composition applied to the substrate to form a fluoropolymer coating on the substrate.

FIELD OF INVENTION

This invention relates to fluoropolymer coating compositions containinga compatible adhesive polymer.

BACKGROUND OF THE INVENTION

Fluoropolymer films have long been used as a protective and decorativeoverlay for a variety of substrates such as metal, wood, andthermoplastic and thermoset polymers. With its excellent chemicalresistance and weathering properties, a thin layer of fluoropolymer filmcan protect less durable substrates from damage in both exterior andinterior use. In recent years, manufacturers of automobiles,recreational vehicles, sports craft and industrial and farm equipmenthave begun using fluoropolymer film structures to surface selected partsof vehicles and equipment in lieu of paint. Single layer polymer filmand multilayer polymer films have been used.

Fluoropolymer films such as polyvinyl fluoride (PVF), polyvinylidenefluoride (PVDF) polymers and copolymers and blends of acrylic polymersand PVDF are often used in the form of a preformed film to provide theprotective surface layer. Such films are often applied to athermoplastic substrate to form a laminate which is then subjected to athermoforming operation. A wide number of thermoplastic substrates aredesirable for use such as polyolefins, polyesters, nylon, ABS, etc. Morerecently, fluoropolymer films have been recognized as an importantcomponent in photovoltaic modules due to their weather resistance, UVresistance, and moisture barrier properties. When fluoropolymer such asPVF is used as a backing sheet to the module, its propertiessignificantly improve module life, allowing module warranties of up to25 years. Fluoropolymer backing sheets are frequently employed in theform of laminate with polyethylene terephthalate (PET) films, typicallywith the PET sandwiched between two fluoropolymer films.

However, laminates of preformed fluoropolymer films on polymericsubstrates having a bond which will not delaminate after years ofoutdoor exposure are difficult to make. Prior art systems such as U.S.Pat. No. 3,133,854 to Simms, U.S. Pat. No. 5,139,878 to Kim et al., andUS 6,632,518 to Schmidt et al. describe primers and adhesives forpreformed films that will produce durable laminate structures. However,these processes require the application of at least one adhesive layer,or both a primer and adhesive layer, prior to the actual laminationstep. The lamination step then requires the application of heat andpressure to form the laminate. Therefore, prior art laminates usingpreformed fluoropolymer films are expensive to manufacture and/orrequire capital intensive equipment. Because preformed fluoropolymerfilms must have sufficient thickness to provide strength for handlingduring manufacture and subsequent processing, the resulting laminatesmay also incorporate thick expensive layers of fluoropolymer, i.e.,thicker than are necessary for an effective protective layer.

SUMMARY OF THE INVENTION

The invention provides a liquid fluoropolymer coating composition and aprocess for using the composition to make fluoropolymer coated polymericsubstrates. The liquid fluoropolymer composition comprises fluoropolymerselected from homopolymers and copolymers of vinyl fluoride andhomopolymers and copolymers of vinylidene fluoride, solvent, andcompatible adhesive polymer comprising functional groups selected fromcarboxylic acid, sulfonic acid, aziridine, amine, isocyanate, melamine,epoxy, hydroxy, anhydride and mixtures thereof. In the process of theinvention the composition is applied to a polymeric substrate comprisingfunctional groups on its surface that interact with said compatibleadhesive polymer to promote bonding of said fluoropolymer coating tosaid substrate. The solvent is removed from the coating compositionapplied to the substrate to form a fluoropolymer coating on thesubstrate.

The invention enables the production of a fluoropolymer coated polymersubstrate with fewer overall processing steps than manufacturinglaminates with preformed fluoropolymer films while providing the strongadhesion to the substrate and good durability to the fluoropolymercoated substrate. In addition, providing the fluoropolymer in the formof a coating enables thinner fluoropolymer layers if desired to savecost. Employing fluoropolymer coatings also enables the incorporation ofadditives into the fluoropolymer layer tailored to the intended use ofthe fluoropolymer coated substrate, e.g., fillers which improve barrierproperties.

DETAILED DESCRIPTION OF THE INVENTION Fluoropolymers

Fluoropolymers useful in the composition and process in accordance withthe invention are selected from homopolymers and copolymers of vinylfluoride (VF) and homopolymers and copolymers of vinylidene fluoride(VF2) polymer. Preferably, the fluoropolymer is selected fromhomopolymers and copolymers of vinyl fluoride comprising at least 60mole % vinyl fluoride and homopolymers and copolymers of vinylidenefluoride comprising at least 60 mole % vinylidene fluoride. Morepreferably, the fluoropolymer is selected from homopolymers andcopolymers of vinyl fluoride comprising at least 80 mole % vinylfluoride and homopolymers and copolymers of vinylidene fluoridecomprising at least 80 mole % vinylidene fluoride. Blends of thefluoropolymers with nonfluoropolymers, e.g., acrylic polymers, may alsobe suitable for the practice of the invention. Homopolymer polyvinylfluoride (PVF) and homopolymer polyvinylidene fluoride (PVDF) are wellsuited for the practice of the invention.

For the practice of the invention with VF copolymers or VF2 copolymers,comonomers can be either fluorinated or nonfluorinated or mixturesthereof. By the term “copolymers” is meant copolymers of VF or VF2 withany number of additional fluorinated monomer units so as to formdipolymers, terpolymers, tetrapolymers, etc. If nonfluorinated monomersare used, the amount used should be limited so that the copolymerretains the desirable properties of the fluoropolymer, i.e., weatherresistance, solvent resistance, barrier properties, etc. Preferably,fluorinated comonomers are used including fluoroolefins, fluorinatedvinyl ethers, or fluorinated dioxoles. Examples of useful fluorinatedcomonomers include tetrafluoroethylene (TFE), hexafluoropropylene (HFP),chlorotrifluoroethylene (CTFE), trifluoroethylene,hexafluoroisobutylene, perfluorobutyl ethylene, perfluoro (propyl vinylether) (PPVE), perfluoro (ethyl vinyl ether) (PEVE), perfluoro (methylvinyl ether) (PMVE), perfluoro-2,2-dimethyl-1,3-dioxole (PDD) andperfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD) among many others.

Homopolymer PVDF coatings can be formed from a high molecular weightPVDF. Blends of PVDF and alkyl (meth)acrylates polymers can be used.Polymethyl methacrylate is particularly desirable. Typically, theseblends can comprise 50-70% by weight of PVDF and 30-50% by weight ofalkyl (meth)acrylate polymers, preferably, polymethyl methacrylate. Suchblends may contain compatibilizers and other additives to stabilize theblend. Such blends of polyvinylidene fluoride, or vinylidene fluoridecopolymer, and acrylic resin as the principal components are describedin U.S. Pat. Nos. 3,524,906; 4,931,324; and 5,707,697.

Homopolymer PVF coatings can be formed from a high molecular weight PVF.Suitable VF copolymers are taught by U.S. Pat. Nos. 6,242,547 and6,403,740 to Uschold.

Compatible Adhesive Polymers

The compatible adhesive polymers employed in the fluoropolymer coatingcomposition according to the invention comprise functional groupsselected from carboxylic acid, sulfonic acid, aziridine, amine,isocyanate, melamine, epoxy, hydroxy, anhydride and mixtures thereof.The compatible adhesive polymer preferably has (1) a backbonecomposition that is compatible with the fluoropolymer in the compositionand (2) pendant functionality capable of reacting with complementaryfunctional groups on a substrate surface. The compatibility of theadhesive polymer backbone with the fluoropolymer will vary but issufficiently compatible so that the adhesive polymer can be introducedinto the fluoropolymer in the desired amount to secure the fluoropolymercoating to the substrate. In general however, homo and copolymersderived largely from vinyl fluoride and vinylidene fluoride will showcompatibility characteristics that will favor acrylic, urethane,aliphatic polyester, polyester urethane, acrylamide, urea andpolycarbonate backbones having the functional groups described above.

The free radical addition polymers derived from acrylic and acrylamidemonomers are well suited to the introduction of pendant functionalgroups using the wealth of functional monomers available. Somerepresentatives include glycidyl acrylate and methacrylate for theintroduction of epoxy groups. These can then be converted into reactiveaminoalcohol groups by reaction of the epoxy functional acrylic withammonia or primary alkylamines. Carboxylic acid, isocyanate, hydroxy andanhydride functionalities are all available using acrylic/methacrylicacid, isocyanatoethyl methacrylate, hydroxyethyl methacrylate or maleicanhydride respectively. Numerous other functional monomers are availablefor functional group introduction as is well known in the art.

Preferred compatible adhesive polymers are amine functional polymers,more preferably, amine functional acrylic polymers.

Pigments and Fillers

If desired, various color, opacity and/or other property effects can beachieved by incorporating pigments and fillers into the fluoropolymercoating composition dispersion during manufacture. Pigments preferablyare used in amounts of about 1 to about 35 wt % based on fluoropolymersolids. Typical pigments that can be used include both clear pigments,such as inorganic siliceous pigments (silica pigments, for example) andconventional pigments. Conventional pigments that can be used includemetallic oxides such as titanium dioxide, and iron oxide; metalhydroxides; metal flakes, such as aluminum flake; chromates, such aslead chromate; sulfides; sulfates; carbonates; carbon black; silica;talc; china clay; phthalocyanine blues and greens, organo reds; organomaroons and other organic pigments and dyes. Preferred are pigments thatare stable at high temperatures during processing. It is also preferablethat the type and amount of pigment is selected to prevent anysignificant adverse affects on the desirable properties of fluoropolymercoating, e.g., weatherability.

Pigments can be formulated into a millbase by mixing the pigments with adispersing resin that may be the same as or compatible with thefluoropolymer composition into which the pigment is to be incorporated.Pigment dispersions can be formed by conventional means, such as sandgrinding, ball milling, attritor grinding or two-roll milling. Otheradditives, while not generally needed or used, such as fiber glass andmineral fillers, anti-slip agents, plasticizers, nucleating agents, andthe like, can be incorporated.

UV Additives and Thermal Stabilizers

The fluoropolymer coating compositions may contain one or more lightstabilizers as additives. Light stabilizer additives include compoundsthat absorb ultraviolet radiation such as hydroxybenzophenones andhydroxybenzotriazoles. Other possible light stabilizer additives includehindered amine light stabilizers (HALS) and antioxidants. Thermalstabilizers can also be used if desired.

Barrier Particles

In a preferred embodiment, the fluoropolymer coating compositionincludes barrier particles. Preferably, the particles areplatelet-shaped particles. Such particles tend to align duringapplication of the coating and, since water solvent and gases such asoxygen cannot pass readily through the particles themselves, amechanical barrier is formed in the resulting coating which reducespermeation of water, solvent and gases. In a photovoltaic module, forexample, the barrier particles substantially increase the moisturebarrier properties of the fluoropolymer and enhance the protectionprovided to the solar cells. If used, barrier particles are preferablypresent in the amount of about 0.5 to about 10% by weight based on thetotal dry weight of the fluoropolymer composition in the coating.

Examples of typical platelet shaped filler particles include mica, glassflake and stainless steel flake, and aluminum flake. The platelet shapedparticles are preferably mica particles, including mica particles coatedwith an oxide layer such as iron or titanium oxide. These particles havean average particle size of about 10 to 200 μm, preferably 20-100 μm,with no more than 50% of the particles of flake having average particlesize of more than about 300 μm. The mica particles coated with an oxidelayer are described in U.S. Pat. Nos. 3,087,827 (Klenke and Stratton);3,087,828 (Linton); and 3,087,829 (Linton). The micas described in thesepatents are coated with oxides or hydrous oxides of titanium, zirconium,aluminum, zinc, antimony, tin, iron, copper, nickel, cobalt, chromium,or vanadium. Mixtures of coated micas can also be used.

Fluoropolymer Coating Composition Formulation

The fluoropolymer coating compositions may contain the fluoropolymereither in the form of a solution or dispersion of the fluoropolymer.Typical solutions or dispersions for the fluoropolymer are preparedusing solvents which have boiling points high enough to avoid bubbleformation during the film forming/drying process. For polymers indispersion form, a solvent which aids in coalescence of thefluoropolymer is preferable. The polymer concentration in thesesolutions or dispersions is adjusted to achieve a workable viscosity ofthe solution and will vary with the particular polymer, the othercomponents of the composition, and the process equipment and conditionsused. Preferably, for solutions the fluoropolymer is present in anamount of about 10 wt % to about 25 wt % based the total weight of thecomposition. For dispersions, the fluoropolymer is preferably present inan amount of about 25 wt % to about 50 wt % based the total weight ofthe composition.

The form of the polymer in the coating composition is dependent upon thetype of fluoropolymer and the solvent used. Homopolymer PVF is normallyin dispersion form. Homopolymer PVDF can be in dispersion or solutionform dependent upon the solvent selected. For example, homopolymer PVDFcan form stable solutions at room temperature in many polar organicsolvents such as ketones, esters and some ethers. Suitable examplesinclude acetone, methylethyl ketone (MEK) and tetrahydrofuran (THF).Depending upon comonomer content and the solvent selected, copolymers ofVF and VF2 may be used either in dispersion or solution form.

In one preferred form of the invention using homopolymer polyvinylfluoride (PVF), suitable coating formulations are prepared usingdispersions of the fluoropolymer. The nature and preparation ofdispersions are described in detail in U.S. Pat. Nos. 2,419,008;2,510,783; and 2,599,300. Preferred PVF dispersions are formed indimethyl acetamide, propylene carbonate, γ-butyrolactone, N-methylpyrrolidone, and dimethylsulfoxide.

To prepare the fluoropolymer coating composition in dispersion form, thefluoropolymer and the compatible adhesive polymer and, optionally one ormore dispersants and/or pigments, are generally first milled together ina suitable solvent. Alternatively, the various components are milled orappropriately mixed separately. Components which are soluble in thesolvent such as the compatible adhesive polymer do not require milling.

A wide variety of mills can be used for the preparation of thedispersion. Typically, the mill employs a dense agitated grindingmedium, such as sand, steel shot, glass beads, ceramic shot, Zirconia,or pebbles, as in a ball mill, an ATTRITOR® available from UnionProcess, Akron, Ohio, or an agitated media mill such as a “Netzsch” millavailable from Netzsch, Inc., Exton, Pennsylvania. The dispersion ismilled for a time sufficient to cause deagglomeration of the PVF.Typical residence time of the dispersion in a Netzsch mill ranges fromthirty seconds up to ten minutes.

The adhesive polymer is employed in the coating composition at a levelsufficient to provide the desired bonding to the polymeric substrate butbelow the level at which the desirable properties of the fluoropolymerwould be significantly adversely affected. Preferably, coatingcomposition contains about 1 to about 40 wt % adhesive polymer, morepreferably about 1 to about 25 wt % adhesive polymer, and mostpreferably 1 to about 20 wt % adhesive polymer, based on the weight ofthe fluoropolymer.

Substrates and Primers

Polymeric substrates used in this invention may be selected from a widenumber of polymers with thermoplastics being preferred. The polymericsubstrate comprises functional groups on its surface that interact withthe compatible adhesive polymer to promote bonding of the fluoropolymercoating to the substrate. The polymeric substrate is preferably apolyester, and more preferably a polyester selected from the groupconsisting of polyethylene terephthalate, polyethylene naphthalate and acoextrudate of polyethylene terephthalate/polyethylene naphthalate. Thepolymer substrate is preferably in the form of a film.

Fillers may also be included in the substrate, where their presence mayimprove the physical properties of the substrate, for example, highermodulus and tensile strength. They may also improve adhesion of thefluoropolymer to the substrate. One exemplary filler is barium sulfate,although others may also be used.

The surface of the polymeric substrate which is to be coated maynaturally possess functional groups suitable for bonding as in hydroxyand/or carboxylic acid in a polyester film or amine and/or acidfunctionality in a polyamide film. Many polymeric substrates may need orwould further benefit from activation however, and this may be achievedby surface treatment. That is, the surface can be made receptive byforming functional groups of carboxylic acid, sulfonic acid, aziridine,amine, isocyanate, melamine, epoxy, hydroxy, anhydride and/or mixturesthereof on the surface. The activation can be achieved by chemicalexposure such as to a gaseous Lewis acid, such as BF₃ or to sulfuricacid or to hot sodium hydroxide. Preferably, the surface can beactivated by exposing one or both surfaces to an open flame whilecooling the opposite surface. Activation can also be achieved bysubjecting the film to a high frequency, spark discharge such as coronatreatment or atmospheric nitrogen plasma treatment.

In a preferred embodiment of this invention, a primer layer is depositedon the polymer substrate and provides the functional groups thatinteract with the compatible adhesive polymer in the fluoropolymercoating composition to promote bonding of the fluoropolymer coating tothe substrate. Suitable primers may include polyamines, polyamides,acrylamide polymers (especially amorphous acrylamides),polyethyleneimines, ethylene copolymers or terpolymers, acid-modifiedpolyolefins (e.g. maleated polyolefins), acrylate or methacrylatepolymers (e.g., emulsion polymers), polyester (e.g., dispersions),polyurethanes (e.g., dispersions), epoxy polymers, epoxyacrylicoligomers, and mixtures thereof. An example of this is the introductionof amine functionality by the application of a polyethyleneimine primercoating. A second example is coextrusion of an acid or anhydridefunctional thermoplastic polymer, such as the polymer sold by the DuPontCompany under the trademark BYNEL®, with the base PET substrate. Whenprimers are used on, for example, PET film substrates which arestretched during manufacture, the primer can be applied either before orafter the film substrate has been stretched.

Coating Application

The fluoropolymer compositions in accordance with the present inventioncan be applied as a liquid directly to suitable polymeric substrates byconventional coating means with no need to form a preformed film.Techniques for producing such coatings include conventional methods ofcasting, dipping, spraying and painting. When the fluoropolymer coatingcontains fluoropolymer in dispersion form, it is typically applied bycasting the dispersion onto the substrate, using conventional means,such as spray, roll, knife, curtain, gravure coaters, or any othermethod that permits the application of a uniform coating without streaksor other defects. Spray and roller applications are the most convenientapplication methods. The dry coating thickness of cast dispersion ispreferably about 2.5 μm (0.1 mil) and about 250 μm (10 mils), preferablybetween about 13 μm (0.5 mil) to about 130 μm (5 mils).

After application, the wet solutions or dispersion are dried to removethe solvent and coalesced thermally if necessary to form thefluoropolymer coating on the substrate. With some compositions in whichthe fluoropolymer is in solution form, the compositions can be coatedonto substrates and allowed to air dry at ambient temperatures. Althoughnot necessary to produce a coalesced film, heating is generallydesirable to dry the coating more quickly. Drying temperature thuspreferably in the range of about 25° C. (ambient conditions) to about200° C. (oven temperature—the film temperature will be lower). Thetemperature used should also be sufficient to promote the interaction ofthe functional groups in the adhesive polymer with the functional groupsof the polymeric substrate to provide secure bonding of thefluoropolymer coating to the substrate. This temperature varies widelywith the adhesive polymer employed and the functional groups ofsubstrate and can range from room temperature to oven temperatures inexcess of that required for the coalescence of fluoropolymers indispersion form as discussed below.

When the fluoropolymer in the composition is in dispersion form, it isnecessary for the solvent to be removed and also for the fluoropolymerto be heated to a sufficiently high temperature that the fluoropolymerparticles coalesce into a continuous film. Preferably, fluoropolymer inthe coating is heated to temperature of about 150° C. to about 250° C.The solvent used preferably aids in coalescence, i.e., enables a lowertemperature to be used for coalesce than would be necessary with nosolvent present. Thus, the conditions used to coalesce polymer will varywith the fluoropolymer used, the thickness of the cast dispersion andthe substrate film, and other operating conditions. For homopolymer PVFcoatings and residence times of about 1 to about 3 minutes, oventemperatures of about from 340° F. (171 ° C.) to about 480° F. (249° C.)can be used to coalesce the film, and temperatures of about 380° F.(193° C.) to about 450° F. (232° C.) have been found to be particularlysatisfactory. The oven air temperatures, of course, are notrepresentative of the temperatures reached by the fluoropolymer coatingwhich will be lower.

In a preferred form of the invention, the fluoropolymer coatingcomposition is applied to a substrate film. Preferably, the substratefilm includes a primer layer providing functional groups that interactwith said compatible adhesive polymer to promote bonding. Preferably,the substrate film is polyester such a polyethylene terephthalate,polyethylene napthalate or a coextrudate of polyethyleneterephthalate/polyethylene naphthalate. In another preferred form of theinvention, the fluoropolymer coating is applied to both surfaces of thesubstrate film. This can be performed simultaneously on both sides ofthe polymeric substrate or alternately, the coated substrate can bedried, turned to the uncoated side and resubmitted to the same coatinghead to apply coating to the opposite side of the film to achievecoating on both sides of the film.

Photovoltaic Modules

Fluoropolymer coated films made in accordance with the invention areespecially useful in photovoltaic modules. A typical construction for aphotovoltaic module includes a thick layer of glass as a glazingmaterial. The glass protects solar cells comprising crystalline siliconwafers and wires which are embedded in a moisture resisting plasticsealing compound such as cross-linked ethylene vinyl acetate.Alternatively thin film solar cells can be applied from varioussemiconductor materials, such as CIGS (copper-indium-gallium-selenide),CTS (cadmium-tellurium-sulfide), a-Si (amorphous silicon) and others ona carrier sheet which is also jacketed on both sides with encapsulantmaterials. Adhered to the encapsulant is a backsheet. Fluoropolymercoated films made in accordance with the invention are useful for suchbacksheets. The fluoropolymer coating comprises fluoropolymer selectedfrom homopolymers and copolymers of vinyl fluoride and homopolymers andcopolymers of vinylidene fluoride polymer blended with compatibleadhesive polymer containing functional groups selected from carboxylicacid, sulfonic acid, aziridine, anhydride, amine, isocyanate, melamine,epoxy, hydroxy, anhydride and mixtures thereof. The polymeric substratefilm comprises functional groups on its surface that interact with thecompatible adhesive polymer to promote bonding of the fluoropolymercoating to the substrate film. The polymeric substrate film ispreferably a polyester, and more preferably a polyester selected fromthe group consisting of polyethylene terephthalate, polyethylenenaphthalate and a coextrudate of polyethylene terephthalate/polyethylenenaphthalate. Polyester provides electrical insulation and moisturebarrier properties, and is an economical component of the back sheet.Preferably both surfaces of the polymeric substrate film is coated withfluoropolymer creating a sandwich of polyester between two layers ofcoating of fluoropolymer. Fluoropolymer films provide excellentstrength, weather resistance, UV resistance, and moisture barrierproperties to the backsheet.

EXAMPLES Test Methods 180 Degree Peel Strength

Peel strengths are measured using a Model 4201 Instron at 2″/min,recording the peak value and averaging 3 samples (ASTM D1876-01 T-PeelTest). If samples easily peeled by hand during the peel initiation stepa value of 0 was recorded.

Humidity Cabinet Peel Test

After removal from the humidity cabinet the samples are scored with arazor knife and a straight edge to produce ¼″ wide strips. The 1″overhang is used as a handle and this tab is pulled at roughly a 180degree angle with slow even tension until either the film breaks or apeel results. Film breaks and peels at either the EVA/glass orEVA/fluoropolymer coating interfaces are considered passing results.Peels between the fluoropolymer coating and the PET substrate areconsidered failures.

Cross-Hatch Adhesion

After removal from the humidity cabinet the samples are scored with arazor knife, aided by a stainless steel template, to make 11 parallelcuts about 3/32 inch (2.4 mm) apart through the film to the glasssurface. This procedure is repeated at right angles to the first cuts toproduce a grid of 100 squares. A strip of transparent tape (3M Brand No.467 PSA tape), 0.75 by 2.16 inch (1.9 by 5.5 cm), is pressed firmly overthe scribed area with the tape oriented in a parallel direction to thescribed lines. The tape is then pulled off at a 90° angle rapidly butwithout jerking. Any failure between the fluoropolymer coating and thePET substrate is considered a failure.

Water Vapor Transmission Rate (WVTR)

Water Vapor Transmission Rate is measured using a Mocon Permatron-W® 700Instrument at 37.8° C. and a permiant relative humidity of 100%.

Examples 1-5

Examples 1 to 5 illustrate bonding PVF based coatings containing anamine functional acrylic adhesive or an epoxy functional acrylicadhesive being used to coat polyethylene terephthalate (PET) filmspreviously primed with either polyethyleneimine (PEI) or ethyleneacrylic acid copolymer (EAA). Results show that in general more adhesivepolymer is better. Results indicate that no significant bonding isachieved in the absence of the adhesive polymer.

PVF based Coating Formulations

TABLE 1 Fluoropolymer Coating Formulations Wt % Amount Adhesive PVFAdhesive Adhesive based Formulation Dispersion* Polymer** Polymer on PVFA 20.0 Amine functional 2.8 10 acrylic B 20.0 Amine functional 5.6 20acrylic C 20.0 Epoxy functional 2.2 10 acrylic D 20.0 Epoxy functional4.4 20 acrylic E 20.0 None 0 0 *PVF (available from DuPont) previouslydispersed into propylene carbonate (available from Huntsman) at 42%solids **amine functional acrylic is methylmethacrylate/2-hydroxy-3-aminopropyl methacrylate 97.8/2.2 at 30% solidsin 2-propanol/toluene 55/45. **Epoxy functional acrylic is methylmethacrylate/glycidyl methacrylate 98/2 at 38% solids in2-propanol/toluene 55/45.

PET+Primer Substrates

TABLE 2 Substrates with PEI Coatings PET thickness Coating Substrate(microns) PEI Thickness (nm) Sample 1 100 Lupasol ® P 20 Sample 2 100Lupasol ® SKA 20 Sample 3 100 Lupasol ® SKA 40

TABLE 3 Substrates with EAA Coatings Substrate PET thickness (microns)Coating Thickness (nm) Sample 4 100 40 Sample 5 100 80

Procedure

-   1. Ingredients of Table 1 are combined and agitated 15 minutes on a    paint shaker to mix.-   2. Draw downs of the mixtures in Table 1 are prepared on each of the    4 mil PET webs in Tables 2 and 3 using a 12 mil draw down knife to    produce approximately 1.2 mil dry fluoropolymer coatings.-   3. A heavy bead of pure PVF dispersion (42% in propylene carbonate)    is applied along 1 edge of the wet draw down to help facilitate peel    testing.-   4. The coated webs are clamped into metal frames and placed into    preheated ovens at either 200 C or 220 C for 3 minutes.-   5. The coalesced and dried films are removed from the ovens and    allowed to cool.-   6. One inch strips are cut perpendicular to the heavy PVF bead.-   7. A scalpel is used to initiate peeling at the PVF bead.-   8. Peel strengths are measured using a Model 4201 Instron at 2″/min,    recording the peak value and averaging 3 samples (ASTM D1876-01    T-Peel Test). If samples easily peeled by hand during the peel    initiation step a value of 0 was recorded.

TABLE 4 Peel Testing Results 200 C. 220 C. Bake Bake Temp Temp PeelFluoropolymer Peel Strength Strength Example Substrate Formulation(KG/in) (KG/in) 1A Sample 1 A 0 0 1B Sample 1 B 0 0.76 1C Sample 1 C 0 01D Sample 1 D 1.18 1.14* 1E Sample 1 E 0 0 2A Sample 2 A 0.78 0.57 2BSample 2 B 1.2 1.47 2C Sample 2 C 0 0 2D Sample 2 D 1.46 1.28* 2E Sample2 E 0 0 3A Sample 3 A 0 0.59 3B Sample 3 B 1.36 1.26 3C Sample 3 C 0 03D Sample 3 D 1.48 1.42* 3E Sample 3 E 0 0 4A Sample 4 A 1.39 1.44 4BSample 4 B 1.53 1.33 4C Sample 4 C 0 1.07 4D Sample 4 D 1.29 1.35* 4ESample 4 E 0 0 5A Sample 5 A 1.15 1.35 5B Sample 5 B 1.44 1.59 5C Sample5 C 1.2 1.13 5D Sample 5 D 0 1.38* 5E Sample 5 E 0 0 *denotesformulation/substrate/bake temperature combinations that survive the1000 hr 85° C./85% humidity cabinet test (only selected samples aretested).

Humidity Cabinet Testing Sample Preparation

Fluoropolymer coated PET substrates are prepared in the same manner asthose of examples 1 through 5 with the exception that the edge bead ofstep 3 was omitted. After removing the samples from the oven andallowing them to cool, the fluoropolymer coating side is corona treatedusing a hand held lab corona treater. The corona treated sample was thenlaminated to a glass panel (4″×8″×⅛″) using the following procedure.

The following sandwich is placed on a vacuum plate with a 1″fluoropolymer coated PET overhang:

fluoropolymer coated PET film with fluoropolymer coating face down

reactive EVA film

glass panel

-   -   1. The sandwich is centered and covered with a silicone rubber        pad    -   2. A metal frame is placed on the rubber pad and vacuum applied        for 20 minutes    -   3. The sandwich+vacuum plate is placed into a room temperature        oven and heating begun to a target of 150° C.    -   4. The sample is held at 150° C. for 20 minutes    -   5. The sample is removed from the oven, vacuum released and        allowed to cool    -   6. The resulting laminates are placed into a paint sample rack        in a humidity cabinet controlled at 85° C./85% humidity.    -   7. Samples are exposed to the humidity cabinet for 1000 hours        and then examined for adhesion using both peel testing and a        cross hatch tape test.

Examples 6-9

Examples 6-9 illustrate PVF coating compositions containing an aminefunction acrylic adhesive being used to coat PET films primed withpolyallylamine primer.

Example 6

Example 6 illustrates the application of a white PVF coating to bothsides of unpigmented and pigmented PET film primed with a polyallylamineprimer.

A white PVF coating formulation is prepared from the formula in thefollowing Table 5. The thermal stabilizer solution listed in Table 5 isprepared from 4.0 wt % Irganox® 1035 (Ciba), 1 wt % Weston® THOP(Crompton) and 95 wt % propylene carbonate. The amine function acrylicpolymer solution listed in Table 5 is prepared by post reacting methylmethacrylate/glycidyl methacrylate (98/2) with ammonia to convert theglycidyl groups into 2-hydroxy-3-aminopropyl groups to produce a primaryamine functional acrylic polymer in a solvent of toluene andisopropanol.

TABLE 5 Ingredient Wet wt. Dry wt. Wt % based on PVF PVF dispersion (40%in PC) 58.55 23.42 N.A. White pigment dispersion 23.55 10.65 45.5Thermal stabilizer sol'n 2.9 0.15 0.66 Amine functional acrylic sol'n14.43 4.32 18.4

Using a doctor blade, the white PVF coating formulation is coated on a 2mil unpigmented PET film primed with a polyallylamine primer and onbarium sulfate pigmented 3.8 mil wide PET film primed with apolyallylamine primer. The coatings are baked in a preheated oven for 10min at 200° C. for 10 minutes. The cooled coated films are then coatedon the opposite side with the same PVF formulation and are baked 15 minat 200° C. Table 6 shows the range of resultant dry film thicknesses forcoatings on pigmented and unpigmented PET films:

TABLE 6 film thickness (mils) sample PET Pigmented? PET 1st PVF Coating2nd PVF Coating 1 Yes 3.8 1 0.7 2 Yes 3.8 1.2 1.5 3 No 2 1 1 4 No 2 1.21.3 5 No 2 1 1 6 No 2 1.2 1.3 7 Yes 3.8 0.7 1 8 Yes 3.8 1.2 1

Example 7

Example 7 illustrates the application of a PVF coating containingpearlescent barrier particles of mica to both sides of unpigmented andpigmented PET film primed with a polyallylamine primer.

A pearlescent PVF coating formulation is prepared from the formula inthe following Table 7:

TABLE 7 Wt % PVF Dispersion 43.03 Mearlin ® Sparkle 139P (Englehard)10.63 Themal Stabilizer Solution 2.13 Amine functional acrylic polymersolution 10.63 Propylene Carbonate 33.58

Using a doctor blade, the pearlescent PVF coating formulation is coatedon a 2 mil wide, unpigmented PET film primed with a polyallylamineprimer and on a 3.8 mil wide, barium sulfate pigmented PET film primedwith a polyallylamine primer. These coatings are baked in a preheatedoven for 10 min at 200° C. for 10 minutes. The cooled coated films arethen coated on the opposite side with the same PVF formulation and baked15 min at 200° C. Table 8 shows the range of resultant dry coatingthicknesses:

TABLE 8 film thickness (mils) sample PET Pigmented? PET 1st PVF Coating2nd PVF Coating 1 Yes 3.8 0.8 0.5 2 Yes 3.8 0.7 1 3 Yes 3.8 1 1.7 4 Yes3.8 0.7 1.6 5 Yes 3.8 0.95 1.05 6 Yes 3.8 0.7 1 7 Yes 3.8 1.2 1 8 Yes3.8 1.2 1.1 9 No 2 1 1 10 No 2 0.9 1 11 No 2 1 1 12 No 2 1.3 1.45 13 No2 1.3 1.5

Example 8

In Example 8, the vapor barrier properties of two side coated PET filmsof Example 6 (sample 7) and Example 7 (sample 2) having white pigmentedand mica pigmented fluoropolymer coatings, respectively, are evaluatedby measuring the Water Vapor Transmission Rate (WVTR). Table 9 shows theimprovement of vapor barrier properties when using barrier particlessuch as mica, as indicated by a lower WVTR value.

TABLE 9 PVF/PET/PVF Side 1 Side 2 thicknesses WVTR Pigment Pigment(mils) g/m²/day white white 0.7/3.8/1.0 5.53 pearl pearl 0.7/3.8/1.02.052

Example 9

In Example 9, the shrinkage properties of white two side coated PETsamples made according to Example 6 (sample1) are compared with samplesof PET films with conventional preformed PVF films laminated to bothsides. The former contained a filler (barium sulfate) in the PETsubstrate, while the latter did not. Table 10 shows the measuredshrinkage data at various temperatures.

TABLE 10 ° F. Two side Coated Film Two side Laminated Film % Change inMachine Direction Dimension as a function of Temperature 25 0.000 0.00050 0.000 0.000 100 0.000 −0.084 150 −0.083 −0.669 200 −0.083 −3.177Change in Tranverse Direction Dimension as a function of Temperature 250.000 0.000 50 0.000 −0.083 100 0.084 −0.083 150 0.000 −0.166 200 0.084−2.912 Note: Two side Coated film layer thicknesses (mils) 1/3.8/0.7 Twoside laminated film layer thicknesses (mils) 1.5/3/1.5

Example 10

Example 10 illustrates the application of a white pigmented and anunpigmented polyvinylidene (PVDF) coating to one side of an unpigmentedand a pigmented PET film primed with a polyallylamine primer.

The unpigmented PVDF coating formulation is prepared from the followingcomponents shown in Table 11:

TABLE 11 Material Source Wt % Polyvinylidene Fluoride Aldrich 21.03Amine functional acrylic polymer solution (1) DuPont 32.9 PropyleneCarbonate Huntsman 46.07 (1) Methyl methacrylate/glycidyl methacrylate(98/2) post reacted with ammonia to convert the glycidyl groups into2-hydroxy-3-aminopropyl groups to produce a primary amine functionalacrylic polymer in a solvent of toluene and isopropanol.

The mixture is dispersed on a paint shaker in the presence of 3 mm glassbeads for 10 minutes.

The white pigmented coating formulation is prepared from the followingcomponents shown in Table 12:

TABLE 12 Material Wt % Clear PVDF Formulation 78.32 White dispersion21.68

Using a 7 mil doctor blade, both the clear PVDF formulation and thewhite PVDF formulation are coated on unpigmented 2 mil PET film andpigmented 3.8 mil PET film primed with a polyallylamine primer using a7-mil doctor blade. A comparison 3.8 mil unprimed PET is similarlycoated. The coated films were baked in a preheated 400° F. convectionoven for 5 minutes. After cooling, a scalpel was used to attempt toremove the PVF films from PET films. Both the pigmented and unpigmentedfilms could be peeled from unprimed PET but could not be peeled fromprimed PET.

1. A process for making a fluoropolymer coated polymeric substratecomprising: applying a liquid fluoropolymer coating composition to apolymeric substrate, said fluoropolymer coating composition comprisingfluoropolymer selected from polyvinyl fluoride homopolymers andcopolymers of vinyl fluoride; solvent; and compatible adhesive polymercomprising functional groups selected from carboxylic acid, sulfonicacid, aziridine, amine, isocyanate, melamine, epoxy, hydroxy, anhydrideand mixtures thereof; said polymeric substrate comprising functionalgroups on its surface that interact with said compatible adhesivepolymer to promote bonding of said fluoropolymer coating to saidsubstrate; and removing the solvent from said coating compositionapplied to said substrate to form a fluoropolymer coating on saidsubstrate.
 2. The process of claim 1 wherein said polymeric substrate isfilm.
 3. The process of claim 1 wherein said polymeric substratecomprises a primer layer on its surface providing said functional groupsthat interact with said compatible adhesive polymer to promote bondingof said fluoropolymer coating to said substrate.
 4. The process of claim1 wherein said functional groups on the surface of said polymericsubstrate are selected from carboxylic acid, sulfonic acid, aziridine,amine, isocyanate, melamine, epoxy, hydroxy, anhydride and mixturesthereof.
 5. The process of claim 1 wherein said compatible adhesivepolymer is functional acrylic polymer.
 6. The process of claim 1 whereinsaid fluoropolymer is selected from polyvinyl fluoride homopolymers andcopolymers of vinyl fluoride comprising at least 60 mole % vinylfluoride.
 7. The process of claim 1 wherein said coating compositioncomprises about 1 to about 40 weight % of said compatible adhesivepolymer based on fluoropolymer solids content.
 8. The process of claim 1wherein said coating composition further comprises pigment.
 9. Theprocess of claim 1 wherein said fluoropolymer of said coatingcomposition is in the form of dispersion particles in said solvent andsaid solvent is selected from is selected from dimethylacetamide,propylene carbonate, γ-butyrolactone, N-methylpyrrolidone anddimethylsulfoxide.
 10. The process of claim 1 wherein said removing ofsaid solvent is performed by heating.
 11. The process of claim 2 whereinsaid fluoropolymer coating composition is applied to both surfaces ofsaid substrate film.
 12. The process of claim 1 wherein said polymericsubstrate comprises thermoplastic polyester.
 13. The process of claim 12wherein said thermoplastic polyester of said substrate is selected fromthe group consisting of polyethylene terephthalate, polyethylenenaphthalate, and a coextrudate of polyethyleneterephthalate/polyethylene naphthalate.